The invention is based on an apparatus for active control of body motions in motor vehicles for reducing undesired vehicle motion and improving the comfort of the ride, as defined hereinafter. An essential feature is that as an integral component of the body control, the present invention includes the concept of fast level adjustment, which is obtained in combination with the active control components that provide the control of the body motion in the range of the natural frequency of the vehicle body, from the standpoint of minimum energy consumption.
To provide conventional level adjustment systems, it is known to integrate the level adjustment with the shock absorber in the control situation, in vehicles having steel springs; such a shock absorber pumps up to the desired control height in the vehicle body automatically, for example, and in response to the vertical vehicle motion. In vehicles with air springs, level adjustment can be achieved via suitable external sensors; with the aid of the air spring, which is supplied with a suitably larger quantity of pressure fluid when loaded, finally, it is also known, in vehicles having so-called hydropneumatic suspensions, to provide level adjustment with the aid of a hydraulic final control element. However, it is a common problem to all these known systems that when the load changes only the body position, that is, the height of the vehicle body above the ground, is controlled, and such systems are designed solely for this provision; a suitable control process has an extremely slow course, lasting at least several seconds at minimum and as long as several minutes, so that it is impossible to cancel out dynamic load fluctuations, for instance action upon the current state of the vehicle or rapidly evolving motions of the vehicle body, given the relatively low energy and power needed for such conventional level adjusting systems.
On the other hand, although fully active hydraulic chassis systems enable optimal chassis control in terms of the comfort of the ride and vehicle handling, they nevertheless prove to be unrealistically expensive, and even if replacement components are provided to economize on power, they still have very high power requirements. Such known active systems can also be considered critical from the standpoint of system stability and reliability.
Known equipment with which the spring stiffness in resilient wheel suspension systems in vehicles can be varied automatically or by open-loop control (German Patent Document A 2 604 809; German Patent Document B 1 275 882), adjust the spring stiffness as a function of the vehicle speed and other parameters, by connecting a bellows of variable volume, as a first pressure chamber, to further pressure chambers each having a constant volume, via a passageway, in the case of purely air-type suspension for vehicles (German Patent Document B 1 275 882). A valve that effects progressively greater throttling (to make the suspension more rigid) upon major spring deflection may be provided in the connecting lines between the pressure chambers, or valves that automatically close in one direction are provided, but such valves do not respond to external load and motion parameters with selective triggering. It must therefore be assumed that the known air suspension, with other pressure chambers that can be additionally put into operation, reacts comparatively unspecifically to external conditions, and upon slow motion of the suspension specifies a spring rigidity that generally reacts more softly, then becoming increasingly rigid upon fast or deep spring deflection; clearly, the desired progressive suspension characteristic is also attained by this means.
In contrast to this, in the case of the subject of German Patent Document A 2 604 809, corresponding to the controllable hydropneumatic or pneumatic spring element, the procedure is such that as a function of a trigger circuit reacting to external parameters, a change in volume effected by a control motor takes place in the second pressure chamber, so that depending on the desired suspension behavior (soft or harder), a correspondingly larger or smaller volume is then made available for the pressure equalization, via a connecting line. Since excess pressure fluid is produced if there is a reduction in volume in the second pressure chamber, the known controllable spring element absolutely demands an additional but otherwise independent level adjustment, via which pressure fluid can drain away, which is shown in FIG. 3 of the aforementioned patent reference. Contrarily, FIG. 2 of the reference already discloses closing or opening the connecting line between the two pressure chambers, which then have constant volume, via a final control element (valve) when there is a controllable spring element that in that case is hydropneumatic; the final control element may be a slide and may be driven by a control motor via a drive pinion that meshes with a gear wheel. Then, via a threaded portion, the gear wheel actuates the final control element in the closing or opening direction. Since as in the exemplary embodiment of FIG. 3 referred to earlier, the volumetric change in the second pressure chamber can take place only gradually via a spindle drive of this kind, the overall result is that only slow adjusting motions are possible; fast switches, for instance to react to emergency situations, cannot be achieved, and such adaptations of the suspension in its rigidity behavior can be achieved, at some expense, but only in the way that could also be more simply achieved purely with slow-reaction level control.
Finally, similarly to the exemplary embodiment of FIG. 2 of German Patent Document A 26 04 809, it is already known in German Patent Document A 27 36 026, in an adjustable wheel suspension system for vehicles, to dispose a fast switchover valve between the two pressure chambers, one of which is coupled directly to the wheel motion; this valve makes the total spring rigidity harder to avoid dangerous operating states in motor vehicles (such as impairment of vehicle stability or handling) by disconnecting the connecting line between the two pressure chambers and reopening it if the operating states change. A known adjustable wheel suspension for vehicles of this kind, however, makes do without the ability by adaptive learning behavior to adjust gradually to various operating states of the vehicle, because with a motor vehicle, it must be expected during operation that it will sometimes travel for long periods of time over smooth roads in good repair, such as Autobahns, or on bumpy lanes, thus requiring not only adaptive long-term adjustment of the suspension behavior but also a rapid reaction to possibly lightning-fast changes in operation, such as side wind when traveling over high bridges and the like, or fast cornering; these latter two driving conditions require immediate stiffening of the suspension system.
Means are also generally known for controlling spring stiffness (DE-C 16 30 058), in which two work chambers of a shock absorber or spring strut are connected via external lines to an apparatus that comprises a pump and two reservoirs. Only one-way check valves are provided as valves in the connecting lines to the spring strut. With this kind of apparatus, however, the damper hardness of such a shock absorber cannot be varied, because to do so energy must be supplied from outside--via the pump--which takes place relatively slowly and requires a certain amount of power. In a shock absorber, controlling the damper hardness only is also known from DE-A 33 04 815.
Suspension systems of modern widely-used vehicle types, especially passenger vehicles, are typically optimized in terms of spring hardness and damper hardness, to an average operating situation; parameters are defined structurally, and except for the effects of aging then remain unchanged during driving. However, in extreme operating situations, such as when the vehicle is empty or fully loaded, or when motion parameters of the vehicle are varying (fast cornering, braking, acceleration, smooth Autobahn travel, or the like), this is problematic and in some cases is not optimal.
Furthermore, semiactive dampers of the kind known from German Offenlegungsschrift 36 10 937 can be used in the present invention; they include a cylinder divided by a piston into two work chambers, and open-loop-controlled hydraulic throttle valves are provided for the applicable direction of motion (tension stage, compression stage), connected either in series or in parallel; connected parallel to each of them is a check valve opening in the opposite direction, and all the connections of the valves remote from the work chamber connections are combined; as a result the damping system, overall and separately, undergoes both passive and semiactive damping variation by suitable triggering of the valves. This particular patent document is expressly referred to herein in combination with the present invention, because the inclusion of such semiactive damper elements as described there is also intended supplementally in the present invention as well, as a component of the entire component assembly, to achieve stable system performance and optimal function. This semiactive damping described in German Offenlegungsschrift 36 10 937 can also be attained by using a single control valve, which is either external or integrated in the damper and is in a position to adjust high-frequency damper forces.
Finally, reference is made to a known apparatus for active chassis control in motor vehicles disclosed in German Offenlegungsschrift 37 38 284, which is based on known level adjustment means and includes a first active final control element, acted upon as a function of the relative spring deflection part, for the level adjusting system and a second active final control element, in the form of an active or aforementioned semiactive damper between wheel suspensions and the body; both active final control elements are integrated into a common closed-loop control circuit, which uses both the relative spring deflection path and the vertical absolute speed of the body to trigger the two final control elements, but to do so requires increased energy, so that it is the object of the present invention to create a component assembly that enables active chassis control and simultaneously is suitable for fast level adjustment, or includes this, and then requires only an extremely small amount of power.